Place the almond paste and powdered sugar in an electric mixer with a paddle and beat until combined. Add the corn syrup and continue to beat until well combined. (If your mixer can’t hold that much, work with half of each ingredient at a time.) Turn out onto a clean work surface and knead the marzipan until a smooth dough forms. Line a baking sheet with parchment paper. Use a tablespoon to scoop out portions of the marzipan. Roll into balls and pop onto the baking sheet. Firmly press a pecan into the corner of each ball. Set aside for 4 hours, or until firm.